<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<input id="num" /><br /><br />
		<input type="button" value="1" onclick="one()" />
		<input type="button" value="2" onclick="two()" />
		<input type="button" value="3" onclick="three()" />
		<input type="button" value="C" onclick="qingchu()" />
	<script>
	        var one = function(){
	        	num.value = num.value + "1";
	        };
	        var two = function(){
	        	num.value = num.value + "2";
	        };
	        var three = function(){
	        	num.value = num.value + "3";
	        };
	        var qingchu= function(){
	        	num.value = "";
	        };
	</script>
	</body>
</html>
